This invention relates to the preparation of oxydiphthalic anhydrides, and more particularly to improved phase transfer catalyzed methods for such preparation.
Oxydiphthalic anhydrides, particularly 4,4xe2x80x2-oxydiphthalic anhydride, are important monomers for the preparation of polyetherimides having exceptionally high temperature performance and excellent solvent resistance. These properties are useful in high performance plastics applications such as advanced composites and electronic circuit materials.
A number of publications, chiefly of Occidental Chemical Corporation, describe the preparation of oxydiphthalic anhydrides by the reaction of halophthalic anhydrides with potassium carbonate. Such publications include U.S. Pat. Nos. 4,870,194, 5,021,168 and 5,153,335. Suitable reaction conditions include neat and solvent reactions and the presence of various catalysts, typically phase transfer catalysts such as tetraphenylphosphonium halides, fluorides such as potassium fluoride and cesium fluoride and carboxylic acids and their salts and hydrolysable esters. Many of these catalytic materials are relatively expensive or limited in their effectiveness, and product yields are often undesirably low. Moreover, numerous ambiguities are present in said publications regarding water content of the reaction mixtures and other conditions, making reproducibility questionable.
It is of interest, therefore, to provide a method for oxydiphthalic anhydride preparation which affords high yields and a minimum of by-products, and which is consistently and reproducibly applicable.
The present invention enables the preparation of oxydiphthalic anhydrides with the use of readily available and relatively inexpensive catalytic materials. Said preparation consistently affords high yields of the desired product and is highly reproducible.
In one embodiment the invention is a method for preparing an oxydiphthalic anhydride which comprises contacting, under reactive and substantially anhydrous conditions, at least one halophthalic anhydride with at least one carbonate of the formula M2CO3, wherein M is an alkali metal having an atomic number of at least 19, in the presence of a catalytic proportion of at least one phase transfer catalyst selected from the group consisting of hexaalkylguanidinium halides and xcex1,xcfx89-bis(pentaalkylguanidinium)alkane halides.